This invention relates generally to a steering mechanism for an agricultural tractor in which the front axle is laterally shiftable in response to a steering movement of the steerable wheels and, more particularly, to a tie rod apparatus interconnecting the shiftable front axle and the chassis to transmit steering mechanism movement into axle shifting movement and to provide for an automatic correction of oversteering of the inside wheel during the turning operation.
Tractors, whether used in an agricultural setting or in an industrial setting, typically include a fixed axle through which primary driving power is transferred through fixed wheels rotatably mounted on opposing ends of the fixed axle, and a steering axle having pivotally mounted steerable ground engaging wheels rotatably mounted on the opposing ends thereof to support the chassis of the tractor above the ground. Supplemental driving power is often provided through the steerable ground engaging wheels, while a steering mechanism remotely controllable by the operator from the operator's compartment selectively controls the pivotal movement of the steerable wheels relative to the steering axle.
One such steering mechanism incorporates a transversely disposed, horizontally extending hydraulic cylinder supported by the steering axle and connected to the opposing steerable wheels. This hydraulic cylinder affects pivotal movement of the steerable wheels about their respective pivotal connections to the steering axle by manipulating the pressures in the hydraulic cylinder to effect a transverse displacement of cylinder rod, causing a turning of the wheels.
Due to physical limitations relating to the range of movement of the steering mechanism and to the eventual interference between the steerable wheels and the steering axle or chassis frame, the amount of pivotal movement of the steerable wheels relative to the steering axle is limited by tire size and track setting to a given restricted turning angle. This maximum turning angle defines the minimum turning radius of the tractor for a given chassis clearance width, axle oscillation angle, wheel base length and king pin spacing. The selection of the length of the wheel base, i.e., the distance between the fixed axle and the steering axle, is a compromise between the need to minimize the turning radius and, therefore, minimize the wheel base length, and to maximize ride considerations which require longer wheel base lengths.
These conflicting wheel base requirements can be better resolved by a steering mechanism incorporating a laterally shifting front axle that is movable in response to a corresponding steering movement of the steerable wheels, which will decrease the turning radius of the tractor for any given wheel base length. The mechanism mounting the steerable axle to the vehicle chassis must accommodate the relative lateral movement between the steering axle and the chassis and would preferably maintain the transversely extending axle in a parallel orientation as the axle and chassis move relative to one another in a generally horizontal plane.
The lateral movement of the shiftable axle is preferable automatically accomplished simultaneously and in conjunction with the steering movement imparted to the pivotable wheels by the steering mechanism. Furthermore, oversteering, which occurs when the wheels are pivoted at generally equal angles and, therefore, because of the lateral spacing of the wheels, do not end up with coinciding turning centers, is a problem with steering mechanisms that needs correction as the wheels are being steered.